Intra-arterial pressure, baroreflex sensitivity and the baroreflex set point were measured in eight patients with essential hypertension during a control period and then after acute treatment (2 h after a 30 mg oral dose) and after chronic treatment (at least 2 months) with nicardipine hydrochloride, a calcium channel antagonist. Mean intra-arterial blood pressure fell after the acute treatment from 130 +/- 14 (SD) control to 118 +/- 11 mmHg, P less than 0.05, and after chronic treatment to 112 +/- 19 mmHg, P less than 0.05. Heart rate increased from 72 +/- 11 control to 81 +/- 16 beats/min, P less than 0.05, during acute treatment indicating activation of the baroreflex control mechanism, but returned to control values with chronic treatment (72 +/- 11 control vs 69 +/- 9 beats/min chronic), indicating a significant shift to the left of the baroreflex set point. There was no change in baroreflex sensitivity after either acute or chronic treatment (control 4.7, acute 4.3, chronic 5.1 ms/mmHg, P not significant for all values). Nicardipine significantly reduces mean intra-arterial pressure both acutely and chronically; the latter is associated with a return of the heart rate to control values due to resetting of the baroreflex control mechanism.